Definition:

Ptolemy (A.D. c. 90-168) or Claudius Ptolemy [Claudius Ptolemaeus] worked at the Library of Alexandria, Egypt [see map]. His name is a mixture of Greek (Ptolemy) and Roman (Claudius) ones, so it is thought his family was Greek, probably living in Egypt, that at some point had been granted Roman citizenship.

Geography

Ptolemy wrote an 8-volume* work on geography (known as the Geography) that was the definitive work on the topic from the second century until the Renaissance.

Making it more accessible to the European population, from 1406-09, Jacopo Angeli da Scarperia translated Ptolemy's Greek Geography into Latin.

Ptolemy listed about 8000 place names with coordinates so others could use the information to plot their own maps.

Ptolemy developed and explained three different ways to project the spherical world onto a two-dimensional surface. He included topography and was the first to include the grid of lines of latitude and longitude on maps. The standard orientation of maps with north on top comes from him, as well.

The errors in his geography led to Columbus' errors more than a millennium later.

Astonomy

Ptolemy also wrote the Syntaxis, usually called Almagest, on astronomy, which drew on the works of earlier astronomers, including Hipparchus. Ptolemy's astronomy was geocentric, with the sun, moon, and planets going around the earth in circular orbits. Despite its inability to make accurate predictions (because of its errors), it remained the definitive work until the 15th century astronomer Copernicus.

Other Areas of Scholarship

Ptolemy also wrote the Tetrabiblos (Four Books), on astrology, and the Optics.

* The eighth volume was probably written earlier and some sources don't appear to count it, so you may see seven-volumes rather than eight.

Sources:

• "Ptolemy" A Dictionary of Scientists. Oxford University Press, 1999.
• Ptolemy from Geography at About.com
• Ptolemy's Geography - Vatican Collection
• CSIS Classics Ptolemy

Read more about Ptolemy and other ancient scientists in Discoveries in Science Made by Ancient Greek Scientists.

Go to Other Ancient / Classical History Glossary pages beginning with the letter

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Alternate Spellings: Claudius Ptolemaeus